$color:red;
div{
    p{
        color: $color;
        display: flex;
    }
}
.box{
    font-size: 20px;
    text-align: center;
    letter-spacing: normal;
    p{

        @extend .box
    }
}
@if(ture){
    p{
        color:red
    }
}
@for $i from 1 to 4 {
    p#{$i}{
        width: 10px *$i;
        height: 30px;
        background-color: red;
    }
}
@for $j from 1 through 4 {
    p#{$j}{
        width: 10px *$j;
        height: 30px;
        background-color: yellow;
    }
}
.demo{
    font-size: 10px;
}
.boxx{
    @extend .demo
}